Your skill level is your current proficiency level of a skill, spell,
trade, or tongue. Your character increases these by practice and
training. Each level represents a numerical value that starts at 1
(the first level of Inept) and ends at 25 (Grandmaster). Each skill
level has three ranks before it becomes the next, with exception to
Grandmaster which cannot increase. Due to this, it is possible to
improve without seeing a change to your skill level's adjective.
The descriptions of skill levels are as follows:
Inept Amateur Novice Apprentice Journeyman
Adept Expert Master Grandmaster
* Wizards can only become a grandmaster in a spell if that spell is of
their specialty school (if they have one).